This invention relates generally to magnetic disk storage systems, and more particularly to write heads having low height, high moment pedestals.
Magnetic disk drives are used to store and retrieve data for digital electronic apparatus such as computers. In FIGS. 1A and 1B, a magnetic disk data storage system 10 of the prior art includes a sealed enclosure 12, a disk drive motor 14, one or more magnetic disks 16, supported for rotation by a drive spindle 13 of motor 14, and an actuator 18 including at least one arm 20, the actuator being attached to an actuator spindle 21. Suspensions 22 are coupled to the ends of the arms 20, and each suspension supports at its distal end a read/write head or transducer 24. The head 24 (which will be described in greater detail with reference to FIGS. 2A and 2B) typically includes an inductive write element with a sensor read element. As the motor 14 rotates the magnetic disk 16, as indicated by the arrow R, an air bearing is formed under the transducer 24 causing it to lift slightly off the surface of the magnetic disk 16, or, as is termed in the art, to xe2x80x9cflyxe2x80x9d above the magnetic disk 16. Alternatively, some transducers, known as contact heads, ride on the disk surface. Various magnetic xe2x80x9ctracksxe2x80x9d of information can be written to and/or read from the magnetic disk 16 as the actuator 18 causes the transducer 24 to pivot in a short arc. The design and manufacture of magnetic disk data storage systems is well known to those skilled in the art.
FIG. 2A shows the distal end of the head 24 having a write element 26. The write element 26 is shown enlarged and with portions exposed for clarity. The write element 26 includes a magnetic yoke 28 having an electrically conductive coil 30 passing therethrough.
The write element 26 can be better understood with reference to FIG. 2B, which shows the write element 26 and an integral read element 32 in cross section. The head 24 includes a substrate 34 above which the read element 32 and the write element 26 are disposed. An edge of the read element 32 and of the write element 26 also define an air bearing surface ABS, in a plane 36, which can be aligned to face the surface of the magnetic disk 16 (see FIGS. 1A and 1B). The read element 32 includes a first shield 38, a second shield 40, and a read sensor 42 that is located within a dielectric medium 44 between the first shield 38 and the second shield 40. The most common type of read sensor 42 used in the read/write head 24 is the magnetoresistive (AMR or GMR) sensor, which is used to detect magnetic field signal changes in a magnetic medium by means of changes in the resistance of the read sensor imparted from the changing magnitude and direction of the magnetic field being sensed.
The write element 26 is typically an inductive write element that includes the second shield 40 (which functions as a first pole for the write element) and a second pole 46 disposed above the first pole 40. Since the present invention focuses on the write element 26, the second shield/first pole 40 will hereafter be referred to as the xe2x80x9cfirst polexe2x80x9d. The first pole 40 and the second pole 46 contact one another at a backgap portion 48, with these three elements collectively forming the yoke 28. The combination of a first pole tip portion and a second pole tip portion near the ABS are sometimes referred to as the yoke tip portion 50. A write gap 52 is formed between the first and second poles 40 and 46 in the yoke tip portion 50. The write gap 52 is filled with a non-magnetic, electrically insulating material that forms a write gap material layer 54. This non-magnetic material can be either integral with (as is shown here) or separate from a first insulation layer 56 that lies upon the first pole 40 and extends from the yoke tip portion 46 to the backgap portion 40. The conductive coil 30, shown in cross section, passes through the yoke 28, sitting upon the write gap material 54. A second insulation layer 58 covers the coil and electrically insulates it from the second pole 46.
An inductive write head such as that shown in FIGS. 2A and 2B operates by passing a writing current through the conductive coil 30. Because of the magnetic properties of the yoke 28, a magnetic flux is induced in the first and second poles 40 and 46 by write currents passed through the coil 30. The write gap 52 allows the magnetic flux to fringe out from the yoke 28 (thus forming a fringing gap field) and to cross a magnetic recording medium that is placed near the ABS.
With reference to FIG. 2C, a critical parameter of a magnetic write element is the trackwidth of the write element, which defines track density. For example, a narrower trackwidth can result in a higher magnetic recording density. The trackwidth is defined by the geometries in the yoke tip portion at the ABS. In some newer designs a pedestal 60 is constructed of a high magnetic moment material (high Bsat), having a width W3. The high Bsat pedestal promotes concentration of magnetic flux in the yoke tip region 50 of the write element 26. As can be seen from this view, the first and second poles 40 and 46 can have different widths W2 and W1 respectively in the yoke tip portion 50. The pedestal has a width W3, which in some implementations can have the same width as that of the second pole W1, as when the pedestal is created by a self aligning process.
With reference to FIG. 2B, the fringing gap field of the write element can be further affected by the positioning of the zero throat level ZT. ZT is defined as the distance from the ABS to the first divergence between the first and second pole, and it can be defined by either the first or second pole 40, 46 depending upon which has the shorter pole tip portion. If the first pole 40 includes a pedestal 60, then ZT is usually defined by the pedestal depth. The pedestal provides a well defined ZT. In order to prevent flux leakage from the second pole 46 into the back portions of the first pole 40, it is desirable to provide a zero throat level in a well defined plane which is parallel to the plane of the ABS. Thus, accurate definition of the trackwidth, and zero throat is critical during the fabrication of the write element.
The performance of the write element is further dependent upon the properties of the magnetic materials used in fabricating the poles of the write element. In order to achieve greater overwrite performance, magnetic materials having a high saturation magnetic flux density Bsatare preferred. A common material employed in forming the poles is high Fe content (55 at % Fe) NiFe alloy having a Bsat of about 16 kG. However, high Fe content NiFe alloy has a high magnetostriction constant xcexs (on the order of 10xe2x88x925) which causes undesirable domain formation in the poles. It is known that the domain wall motion in the writer is directly related to the increase in popcorn noise in the read element, especially when the motion occurs in the first pole, which also serves as a shield for the read element.
A reduction in popcorn noise in the read element can be achieved through the use of soft magnetic materials, (i.e. materials having a low magnetostriction constant) in the fabrication of the first pole 40. However, such materials generally have limited Bsat. In order to promote concentration of magnetic flux density in the yoke tip region, a high Bsat material is used to form the pedestal 60.
The size and shape of the pedestal has a dramatic affect on the flow of magnetic flux in the yoke tip region 50. For example, the abrupt angle between the pedestal 60 and the rest of the first pole 40 inhibits flux flow and can lead to choking or saturation of flux. In addition, a thick pedestal (i.e. in the direction from the first pole 40 to the write gap 52) causes further choking of the flux and also leads to poorly defined signal pulses. Therefore, accurate control of pedestal size and shape is critical. Creating a pedestal which is sufficiently thin and also has a desirable shape has been limited by available manufacturing techniques. For example, existing manufacturing techniques which employ CMP can not be used to construct a pedestal with a tightly controlled thickness, thus limiting the pedestal to an overall minimum size.
Therefore, there remains a need for a process for manufacturing a desired thin pedestal. The process would necessarily allow tighter control of thickness than is possible with previous processes and would also allow the shape of the pedestal to be controlled to soften the angle of the transition between the pedestal and the rest of the first pole 40. In addition, the process would allow the pedestal to be constructed of a high Bsat material, many of which materials must be sputter deposited.
The present invention provides a method for manufacturing a write element for use in a magnetic data recording system, the write element having a thin pedestal having a well controlled shape and size. A first pole is constructed of a soft magnetic material. A layer of high Bsat material is then deposited onto the magnetic material of the first pole. A bi-layer photoresist is patterned onto the layer of high Bsat material in a pattern corresponding to the desired pedestal shape. The high Bsat material layer is then etched, forming a pedestal with a tapered edge, by removing material from the region not covered by the bi-layer photoresist. A first insulation layer is then deposited, and the bi-layer photoresist is subsequently lifted off. Thereafter, a layer of write gap material is deposited and an electrically conductive coil is formed on the write gap material. A second insulation layer is applied, and a second pole is formed so as to be electrically connected with the first pole.
The etching can be performed in such a manner that the edge of the pedestal can be a smoothly tapered. This advantageously promotes smooth flux flow through the pole tip region of the first pole. In addition, the process allows the high Bsat material to be sputter deposited. This is advantageous in that currently available high Bsat materials cannot be plated and must, therefore, be sputter deposited.
Another aspect of the invention is that it allows excellent control of pedestal thickness. One reason that the thickness of the pedestal can be tightly controlled is that chemical mechanical polishing is not required. CMP processes remove material in a manner which is difficult to accurately control, and therefore a relatively large tolerance in pedestal thickness would be required if such a process were used.
The bi-layer photoresist includes a first layer and a second layer that covers and extends beyond the edge of the first layer. The portion of the second layer extending beyond the first layer creates an overhang. When the first insulation layer is subsequently applied, the first insulation layer will form a smooth tapered edge terminating beneath the overhang. The termination point of the insulation layer can be controlled by the amount of overhang on the bi-layer photoresist or can also be controlled by the manner in which the first insulation layer is deposited. Although the deposited first insulation layer will cover the photoresist, the portion under the overhang will be accessible to chemicals for lifting off the photoresist.
For a fuller understanding of the nature and advantages of the present invention, reference should be made to the following detailed description taken together with the accompanying figures.